A conventional ejector cycle device is a vapor compression type refrigerator in which a nozzle in its ejector isentropically decompresses and expands a refrigerant to accelerate the refrigerant. A liquid-phase refrigerant separated in a gas-liquid separator is circulated through an evaporator by the pump action of the ejector. A gas-phase refrigerant sucked from the evaporator and the refrigerant injected from the nozzle are mixed while the expansion energy is converted into pressure energy to increase the suction pressure of a compressor.
Then, the refrigerant flowing out of the ejector is separated into the gas-phase refrigerant and the liquid-phase refrigerant by the gas-liquid separator. The liquid-phase refrigerant is subsequently supplied to the side of the evaporator and the gas-phase refrigerant is supplied to the suction side of the compressor. An example of such a refrigerator is disclosed in Japanese Patent Laid-Open Publication No. Hei 5-149652.
Some vapor compression type refrigerators use an expansion valve that causes an isenthalpic (Joule-Thomson) refrigerant expansion. This type of refrigerator utilizes refrigeration oil having a compatibility relative to a carbon dioxide refrigerant at or below a critical pressure that is lower than its compatibility above the critical pressure. An example of such a refrigerator is disclosed in Japanese Patent Laid-Open Publication No. Hei 11-94380.
However, in both vapor compression type refrigerators, refrigeration oil is mixed into the refrigerant and circulated through the cycle to lubricate sliding portions in the compressor. For example, in the ejector cycle device disclosed in Japanese Patent Laid-Open Publication No. Hei 5-149652, the refrigerant flowing out of the ejector is separated into a gas-phase refrigerant and a liquid-phase refrigerant by the gas-liquid separator. The liquid-phase refrigerant is subsequently supplied to the side of the evaporator and the gas-phase refrigerant is supplied to the suction side of the compressor. However, the gas-liquid separator only provides operation of separation between the gas-phase refrigerant and the liquid-phase refrigerant. The gas-liquid separator does not provide separation between the refrigerant and the refrigeration oil. Also, the gas-liquid separator does not supply the suction side of the compressor with the refrigeration oil and the gas-phase refrigerant alone and the evaporator with the liquid-phase refrigerant alone.
When the compressor in the above refrigerator is supplied with a large amount of liquid-phase refrigerant, the pressure inside the compressor may excessively increase and thereby result in damage to the compressor. Further, when the evaporator is supplied with a large amount of refrigeration oil, the refrigeration oil will. adhere to the inner surface of the evaporator and possibly lower the heat transfer rate between the refrigerant and the evaporator and thereby decrease the amount of refrigeration oil returning to the compressor. This may result in problems such as burnt sliding portions in the compressor.
Finally, the gas-liquid separator tends to mix the liquid-phase refrigerant and the refrigeration oil through convection due to such reasons as the dynamic pressure of the incoming refrigerant. Therefore, separating the liquid-phase refrigerant and the refrigeration oil from each other is particularly difficult.